Multianion analysis, applications of ion chromatography - Determination of Anions in Natural and Treated Waters - page 658

a hydrophobic membrane was used to concentrate and separate carboxylic acids from
inorganic salts and most other organic compounds prior to the application of ion
chromatography. Acetic acid, propionic acid, butyric acid-1, butyric acid-2, valeric and
pyruvic acid, acrylic acid and benzoic acid were all found in reasonable concentrations in
sea water.
12.4 Aqueous precipitation
12.4.1 Chloride, bromide, fluoride, nitrate, nitrite, sulphate, sulphite and
phosphate
The application of ion chromatography to the determination of nitrite, nitrate, halogens,
sulphate and phosphate (also caldium and magnesium) sodium and potassium in
rainwater is discussed below. Wetzel et al. [58] used ion chromatography to obtain
determinations down to µg L −1 concentrations of chloride, phosphate, nitrate and
sulphate in rain water samples. Conductivity detector response is linear with
concentrations over the mg L −1 to µg L −1 range for the determinands examined. It was
shown that a 3×50mm pellicular anion-exchange resin with tetraethyl ammonium groups
attached to a styrene divinyl benzene backbone concentrator column can be loaded
remotely and stored for at least 7 days before analysis without significantly affecting
ionic determinations.
The response for phosphate, nitrate and sulphate was linear over four orders of
magnitude (2-10 4 µg L −1 ). Response for chloride ion was linear over three orders of
magnitude (2-103µg L −1 ). Correlation coefficients for a linear least squares fit were
between 0.9877 and 0.9999.
Oikawa and Saitoh [59] reported studies of the application of ion chromatography to
the determination of fluoride, chloride, bromide, nitrite, nitrate, sulphate, sulphite and
phosphate ions in 3ml samples of rainwater. The results show that the most suitable
eluent for this purpose is 2m mol L −1 sodium carbonate/5m mol L −1 sodium hydroxide.
The reproducibility of the determination was satisfactory for standard solutions of all the
ions except for nitrite. This problem was solved by preparing standard and sample
solutions with the same composition as the eluent.
Apparatus
Model 14 ion chromatograph (Dionex Corp.). Perkin Elmer Model Sigma 10 Data
Processor.
Reagents
Sodium carbonate (anhydrous), Merck ultrapure.
Sodium nitrite, Merck Analytical grade. Water, deionised and distilled.
Procedure
Filter the rainwater sample with a membrane filter having a pore size of 0.45µm. Use the
filtrate as the sample for the test. Inject approximately 2ml of the sample into a microloop
with a syringe. Table 12.10 lists the determination conditions. Obtain the peak areas of